The Origin of Life:

Abiogenesis by Chemical Evolution?

How did life begin? What was the origin
of the first carbon-based life on earth?
Scientists are proposing various theories for a natural origin
of life by a process of abiogenesis (a non-biological
production of life) that can be viewed as a chemical
evolution from non-life to life. {note: Another
meaning
of chemical
evolutionis the natural process, occurring in stars, that forms the
nuclei
of
larger
atoms
(Li, C,
N,
O,...)
from
the smaller
nuclei of H and
He. }

Scientists usually propose a four-stage process of formation for the
first life:1A. formation of small organic molecules (amino acids, nucleic acid
bases,…),1B. and these combine to make larger biomolecules (proteins, RNA, lipids,…),2A. which self-organized, by a variety of interactions, into a semi-alive
system2B. that gradually transformed into a more sophisticated form, a living
organism.

Before looking at web-pages with proposals
(and criticisms, as in claims for INTELLIGENT
DESIGN) for various
scientific theories about a natural origin of life, let's get a "big
picture overview" of
some problems and possible solutions:

An Outline of Problems
There are chemistry problems in Stages 1A and 1B,
due to some energetically unfavorable reactions and unproductive competitive reactions.
But the toughest problems are biological, in Stages
2A and 2B, because the simplest possible "living system" seems to require
hundreds of components interacting in an organized way to achieve
self-replication and energy production, and this organized complexity would
have
to
occur before
natural selection (which depends on self-replication) was available. For these stages we can ask, "Are scientists learning that what is required for life is greater than what is possible by natural process?" or is our current knowledge insufficient to answer this question because we don't yet know enough about what is required and what is possible?

Problems and Possible Solutions
For awhile following the Miller-Urey experiments
in 1953, a popular theory proposed that life began in a prebiotic ocean filled
with a "chemical soup" of organic biomolecules. But problems
with this scenario led to proposals for different types of localized environments,
such as an isolated semi-evaporated pond, or a seafloor hydrothermal vent, or
in a location that allowed interactions between
biomolecules and minerals/clays with organizational or catalytic functions. Or
maybe
the
original
abiogenesis
occurred
in a very different environment, on another planet or in space. And although
most science has focused on the familiar life that we observe on earth (based
on carbon, in aqueous solution), maybe the first life had a different chemical
or physical basis.
All proposals for a transition from nonlife to life
must cope with various "chicken and egg" problems. For
example,
all
modern
life involves proteins and
DNA, but the production of protein
requires
DNA, and
the production of DNA requires protein, and both require RNA and more, operating
in a complex coordinated system. Could a simple organism be "alive" with
only proteins, or only DNA? But if it had both, it would not be simple,
and could this complexity arise by chance?
To avoid the need for a complex system with proteins
plus DNA, some scientists have proposed that RNA (which combines the replicating
ability of DNA and catalytic activity of proteins) was the key life-producing
molecule in the earliest living cells. A prebiotic RNA
World is still a popular theory, but questions have arisen due to
the difficulty of RNA synthesis in prebiotic conditions, and because RNA functionality
(in catalytic activity and self-replicating ability) has not matched the initial
optimistic hopes. In response, recent theories have proposed a simpler
pre-RNA
World with key functional roles played by other molecules.
Scientists are trying to develop principles for a
pre-biological selection that was functionally analogous to (although less efficient
than) biological natural selection. And there is a continuing search for
ways to reduce the minimal complexity that would be required for a system with
self-replication (with "genes first") or metabolism (if "metabolism
first") or both. {replication or metabolism, which came first?} But
instead
of
imagining
a simplification, some
scientists are looking toward complexity for answers to abiogenesis, by
proposing that within a complex mixture of chemicals there can be a spontaneous
emergence of an autocatalytic network of reactions that is a self-replicating
system, and the beginning of life.

Current Theories of Abiogenesis

• Word-IQ has an excellent introductory overview, Origin of Life.
• Loren Haarsma & Deborah Haarsma briefly outline theories about The
First Living Cell and explain why "as
long as science does not have a definite conclusion, it would be best
to exercise some humility and caution" in claiming that,
based on what we know from current science, natural abiogenesis is or
isn't possible. And they describe two rational Christian preferences
about future scientific research, hoping that science either will or
won't be more successful in finding a way for life to begin naturally.

According to Biology-Online, biogenesis is "the principle stating that life arises from pre-existing life, not from nonliving material." Until the mid-1860s, this principle was opposed by a theory of spontaneous generation claiming that "complex, living organisms may be produced from nonliving matter. It was a popular belief that mice occur spontaneously from stored grain, or maggots spontaneously appear in meat." Modern theories of abiogenesis (to form the first life) do not oppose biogenesis (which applies to current life) and do not propose spontaneous generation.
• History of Theories: Early theories and experiments, into the 1780s, are
described by Jack
Haas in a historical approach that shows "how vastly different [compared with modern ideas] was the meaning of ‘experiment’ and of ‘scientific work’ in these different times and places." For the rest of the story, you can get a quick overview from Tami Port and more details from John
Wilkins; they explain how clever experiments, leading up to the conclusive demonstrations by Louis Pasteur in the 1860s, showed that spontaneous
generation does not occur now. This history is valuable
for clarifying what modern theories are NOT, so we can avoid strawman misconceptions about current theories of abiogenesis, which (as explained in the ISCID
Encyclopedia) are much more sophisticated than the simple theories of spontaneous generation from the past.

Defenses of Abiogenesis Theories

• In an interview
with Stanley Miller in 1996 we see an optimistic
description of abiogenesis science and its prospects for development,
and Miller concludes with a different perspective (compared with Rana & Ross)
on the relatively small community of research scientists who are focusing
on the origin of life.
• Ian Musgrave criticizes math-based claims for The
Improbability of Abiogenesis because, among other reasons, precise
specificity is not essential for functionality, and a huge number of "chemistry experiments in nature" can
occur simultaneously.
• Talk Origins (Mark Isaak, editor) also has responses to
17 criticisms of abiogenesis, and a links-page for
their Abiogenesis FAQs.
• Also, possible solutions for problems are proposed in the overviews above and
the sections below.

Stage 1A — PreBiotic Chemistry (Miller-Urey and more)
Modern studies of prebiotic (pre-biological)
biochemistry — to
form organic molecules and biomolecules in Stages
1A and 1B — began
in 1953 with the Miller-Urey
Experiment. Early MU experiments used a reducing
atmosphere with reactive chemicals (CH4, H2, and NH3) plus H2O. Within
two decades, most geologists thought the early earth had a non-reducing
neutral atmosphere (mainly CO2 and N2 plus H2O) that was much
less reactive; when
these chemicals were used in later variations of MU the yields of organic
molecules were much lower. But geological questions about earth's
early atmosphere continued through the 1990s, and in 2005 calculations
about gas from chordites indicated that the atmosphere might have
been reducing, similar to the early MUs. Currently the chemistry
of the early atmosphere is in doubt, as described in Wikipedia.
There have been questions about other aspects of
Miller-Urey experiments, such as the choice of energy sources and why newly
formed products were
isolated (before they could be broken down by further reactions), to
ask whether the MUs were realistic simulations of conditions on the early earth.
In response to these questions and their own, researchers
studied a wide variety of Miller-Urey variations, using different reactant
mixtures, energy
sources, and conditions, and in the reaction products they observed a
variety of organic compounds, in amounts that spanned a wide range but usually
were fairly low.
In addition, scientists discovered that objects
from outer space (meteors, comets,…) contain interesting organic compounds, plus H2O, and these
compounds would have become "part of the reaction mixture" when
the space-objects landed on earth.

• On the 50th anniversary of the Miller-Urey publication, a report
from Astrobiology Magazine.
•
For an overview of current views on the early atmosphere, read the section
on "Conditions for Synthesis of Organic Molecules on the Early Earth" in
the page by Moritz.
•
Talk Origins has brief responses about the early atmosphere: A & B.
•
Jeffrey Bada ran a
recent variation of Miller-Urey that produces more amino
acids, but not nucleic acid bases.

Stage 1B — Polymer Chemistry (to make proteins,
RNA,…)
The Miller-Urey experiments are about stage 1A, forming
small organic molecules.
In 1B, problems occur due to energetics — because in water the reactions
to form larger biomolecules (proteins, RNA, and DNA) are energetically
unfavorable — and also due to competition.
For example, during protein synthesis a prebiotic
reaction mixture would contain many different chemicals (L-amino acids
and R-amino acids, plus
many other molecules) and the majority of newly formed bonds would not
be the special peptide bonds (linking only L-amino acids) found in natural
proteins. The scarcity of L-peptide bonds is partly due to the fact that
in a watery "soup" the formation of these bonds is energetically
unfavorable. Therefore, abiogenesis researchers have searched for and studied
non-aqueous reaction sites, such as evaporated ponds or on the surface
of minerals.
Similar difficulties would arise in the prebiotic
formation of other important biomolecules. Problems occur in both
stages of forming RNA, in forming
ribose sugars and some nuclotide bases (in 1A) and connecting these together
(in 1B). The prebiotic synthesis of RNA has been especially unsuccessful,
but perhaps special environments (such as the surface of minerals) could
help with the reactions.

•
In the "General Considerations" section of From
Building Blocks to the Polymers of Life says, "the
formation of either proteins or RNA from their monomers is not energetically
favored… [so]… in
the presence of water… energy input was necessary to have made RNA
and polypeptides on primitive Earth." { Later,
there is more about synthesis problems in an RNA
World. }
•
For possible solutions to another problem, click the link for "Origin
of the Homochirality of Amino Acids & Sugars" in Moritz and read
about a crystal with 10% separation of L & D amino acids.

Stages 2A & 2B — Chemical
Evolution into the First Life
Most scientists think the most challenging problems
for abiogenesis by chemical evolution are biological, in Stages 2A and
2B, because "The
simplest possible ‘living system’ seems to require hundreds of
components interacting in an organized way to achieve self-replication
and energy production, and this organized complexity would have to occur
before natural selection (which depends on self-replication) was available."
What is life? Michael Pidwirny summarizes the
answer given by Daniel Koshland in The
Seven Pillars of Life. But which of these would have been necessary (or useful) during each part
of a natural chemical evolution through stages 2A (semi-alive?) and 2B
into being fully alive? Asking "why is it difficult to define life?" draws
responses, brief (Joel
Achenbach) and in
detail (Carol Cleland & Christopher
Chyba).
What is the minimal complexity required for life?
At the end of his Introduction, Moritz summarizes current ideas: "The most elementary [non-parasitic]
cells we currently know… have 482 protein-coding genes (most bacteria,
such as E. coli, encode for more than 2000 different proteins)" plus
some non-protein molecules; of these, "according to the probably best
experimental study to date (abstract & full
text) the essential ones
are 387" and "the likely most accurate hypothetical study (abstract & full
text) puts the minimal number of genes at 206. All the proteins produced
from these genes are involved in a maze of pathways of metabolism, replication,
as well as building and maintenance of structure, which is of bewildering
complexity."

Gene-First or Metabolism-First?
Scientists currently have two main theories about the first
functionality in the development toward life: Was it genes-first or metabolism-first or
some of each? {some
possibilities} But with either type of
scenario, at some point in its journey toward becoming a living cell it
would need to
construct a membrane to separate itself from the external environment. But, as Richard Deem, explains, there are problems
with a prebiotic synthesis of cell membranes.
•
Leslie Orgel discusses gene-first & metabolism-first theories for a "chemical
evolution" origin of life.

Genes-First
in an RNA World
To avoid the need for a complex system of proteins
plus DNA (with hundreds of proteins required for life) some scientists
have proposed that RNA — which
combines the replicating ability of DNA and catalytic activity of proteins — was
the key life-producing molecule in the earliest living cells.
This common proposal is described in many pages in
other sections, and is the main focus of these pages:
•
Leslie Orgel (1997) proposes a prebiotic RNA World in The
Origin of Life on Earth.
• What can RNA do? Jack Szostak is exploring the possibilities,
in an attempt to produce RNA-life
in the lab.
•
Richard Deem looks at problems
(synthesis,…) of an RNA World and so do others, including Robert Shapiro ( 12 )and Gordon
Mills & Dean Kenyon.
•
Recently, scientists determined the
3-D structure of a ribozyme (an RNA
enzyme).

Metabolism-First with Chemical Reactions
Some scientists think life was an emergent property
that happened, either gradually or suddenly, due to interactions between
chemicals in a complex
system. A "metabolism first" view is an approach, not a specific
theory, and various advocates propose different chemical mixtures and reaction
locales:
•
An origin of life beginning with small-molecule interactions is described
by Robert Shapiro, briefly and
(after criticizing RNA World) in more detail.
•
Loren Haarsma & Terry Gray briefly outline the basic ideas of abiogenesis
in an autocatalytic system.
• Leslie Orgel, an advocate of genes-first, criticizes metabolism-first. (pro-ID commentary by Casey Luskin)
•
Moritz writes a lot about metabolism-first,
from "Specificity of Chemical Reactions" onward.
•
One possibility, among many, is a hypercycle.
•
Bruce Weber has an outline of ideas about life arising from interactions
in complex systems.
•
Christian De Duve, in 1995, compares an RNA World and Thioester
World.
•
Michael Russell & Allan Hall look at possibilities in warm
underwater springs and converting CO2 into acetate and then life.
• James Ferry & Christopher House study microbes that metabolize carbon
monoxide and they propose a way to reconcile heterotrophic and autotrophic theories
for the origin of life.
• a book review of Genesis: The Scientific Quest for Life's Origins (by Robert Hazen) about emergent
cycles and ocean vents, minerals and more.
• In the late-1980s, Graham Cairns-Smith proposed that
life began as "clay
organisms" that transformed into DNA-based life, but this idea is
not currently popular or influential. A website about the role of
Clays & Crystals in
the Origin of Life includes articles, links, and criticisms; another
critique is from Charles Thaxton & Stephen Meyer.

Panspermia would require an extraterrestrial origin
of life, on another planet or even in space. But a natural abiogenesis
to form life could have occurred only
elsewhere (then brought to earth by panspermia) or only on earth, or both, or neither.
• If astrobiology is to have an empirical basis, scientists and engineers
must ask, How
do we Search for Life in Alien Worlds? and maybe they should consider unusual
un-earthlike environments.
• a book-summary of Bruce Jakosky's Search
for Life on Other Planets
• You can learn about NASA's multi-faceted exobiology programs in a brief abstract and
a multi-part Astrobiology
Roadmap that explains ideas and research strategies, and an overview with "Related
Links"
to explore, including the SETI
Institute (Search
for Extraterrestrial Intelligence).
• paper-summaries (about
astrobiology & astronomy) from Scientific American's Magnificent
Cosmos

Multiverse — Can events that seem extremely improbable happen anyway?
IF a natural origin of life is extremely improbable in our universe, and IF we live in a multiverse containing
an immense number of universes similar to our own (with the same properties of nature), THEN even though
a natural origin seems improbable,
maybe it actually is not improbable. Why? Because if enough universes
exist, even highly improbable events (like a natural origin of life?) will happen somewhere in one or more of the many universes, and evidently — because we are alive — we live in one of those places! This is the logical basis of a claim that a
multiverse is a way to beat the odds for a "fine tuning" of nature, or for events (like the origin of life) that occur during the history of nature.
•
Eugene Koonin claims that although a natural origin of life is highly improbable in our
universe, in a multiverse it would be probable and would occur somewhere, and here is where it happened. You
can read Koonin's
abstract and paper, plus comments (by referees & author) in HTML or PDF.
• OUR UNIVERSE — INTELLIGENT DESIGN and/or MULTIVERSE is a links-page examining claims for a design of nature, and for design-directed action during history as an explanation for features such as the first carbon-based life.

An Overview/Analysis of Views
Let's look at different views of origins, in terms
of possibilities for the origin of the first carbon-based life on earth. Maybe
this origin was natural and a plausible Non-Design theory is possible,
in
principle, and the correct theory: N1) is
currently known (whether or not it currently seems plausible), or N2) will
be known in the future, or N3) will never be known because
the natural process was too complex or unfamiliar or cognitively difficult for
us to propose. But perhaps it's impossible to construct a Non-Design
theory that is plausible (that would have a reasonable probability of happening)
because: N4) the
natural origin was highly improbable even though it did occur, or N4*) the
N4-origin seems improbable but actually is highly probable because we live in
a universe that is one of an immense number of universes in a multiverse that
was either designed or undesigned *. Or
the first earth-life might have been produced by Design-directed action,
with D1) natural
design and construction, or D2) supernatural design and creation. Or
maybe it happened some other way, X. {* All
possibilities — N1 to N4 plus D1, D2, and X — could occur in a
universe (which probably would have to be designed) or
a multiverse (either designed or undesigned). }
In currently conventional science, scientists define
their goal as N1 or N2; those with confidence claim N1 with current plausibility,
those with less confidence claim N1 with current implausibility, or N2, N3, N4,
or X; an appeal to "inevitability in a multiverse" (with low
confidence in abiogenesis theories, but high confidence in multiverse theories)
is N4*; undirected panspermia is N1 (for the "panspermia" claim)
preceded in history by any of the possibilities for the earlier origin, while
directed
panspermia
is
D1 preceded by any possibility; the scientific proposals of Intelligent
Design
are for
"either D1 or D2"; some
creationists
(either
old-earth
or
young-earth) propose direct divine creation by D2, while evolutionary
creationists propose indirect divine creation that is compatible with
any possibility (if it
followed the divine designing and creating of a universe or multiverse that would
naturally produce life) not involving D2; and an atheist,
or a rigid agnostic, can accept any possibility except direct divine creation
(D2) or indirect divine creation.

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which don't necessarily represent the views of the American Scientific Affiliation. Therefore, linking
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This page, written by Craig Rusbult (editor of ASA Science
Ed Website), is
http://www.asa3.org/ASA/education/origins/cheme.htm
and was revised
June 24, 2010
( all links were checked-and-fixed on
July 3, 2006 )